1,364 research outputs found
Two-fermion and Two-photon Final States at LEP2 and Search for Extra Dimensions
No full textFor the first time the experiments ALEPH, DELPHI, L3 and OPAL have presented preliminary results for fermion-pair and photon-pair production in e+e- collisions on the full LEP2 data set. The details of the experimental measurements and results from their LEP-wide combination are presented. No statistically significant deviations from the Standard Model expectations are observed and lower limits, some obtained in dedicated analyses, for new physics phenomena at 95 % confidence level are derived. The scales of contact interactions are constrained to lie above 10-20 TeV, depending on the helicity structure. The Standard Model has thus been tested at LEP2 down to distances 10^{-19} - 10^{-20} m. This has many implications, one example being the interpretation of the new result on the anomalous magnetic moment of the muon as coming from muon substructure. For gamma-gamma final states the QED cut-offs are Lambda_+ > 0.44 TeV and Lambda_- > 0.37 TeV. In a combined analysis, using e+e- and gamma-gamma final states, the most stringent lower limits to date, M_s^+ > 1.13 TeV (lambda = +1) and M_s^- > 1.39 TeV (lambda = -1), on the low gravity effective Planck scale are set. Constrains on the scales of string models like TeV strings and D-branes are derived. In the last case the lower limit is 1.5 - 4 TeV, depending on the coupling strength
Study of Multi-muon Events from EAS with the L3 Detector at Shallow Depth Underground
No full textWe present first preliminary data from the L3+Cosmics experiment and resultsfrom Monte Carlo simulations of multi-muon events as observed 30 m underground.We present first preliminary data from the L3+Cosmics experiment and results from Monte Carlo simulations of multi-muon events as observed 30 m underground
Global Analysis of Bhabha Scattering at LEP2 and Limits on Low Scale Gravity Models
No full textA global analysis of the data on Bhabha scattering from the four LEP experiments ALEPH, DELPHI, L3 and OPAL is performed to search for effects of virtual graviton exchange in models with low scale gravity. No statistically significant deviations from the Standard Model expectations are observed and lower limits on the scale of models with large extra dimensions of for and for at 95% confidence level are derived
Hint for axial-vector contact interactions in the data on at centre-of-mass energies 192-208 GeV
No full textFor the first time the experiments ALEPH, DELPHI, L3 and OPAL have presented preliminary results for fermion-pair production in e+e- collisions on the full data set above the Z pole. A combined analysis of the Bhabha scattering measurements is performed to search for effects of contact interactions. In the case of two axial-vector (AA) currents the best fit to the data is 2.6 standard deviations away from the Standard Model expectation, corresponding to an energy scale TeV for contact interactions. For other models no statistically significant deviations are observed, and the data are used to set lower limits at 95 % confidence level on the contact interaction scales ranging from 8.2 to 21.3 TeV, depending on the helicity structure
Sensitivity to Contact Interactions and Extra Dimensions in Di-lepton and Di-photon Channels at Future Colliders
No full textVirtual effects from a generic description of physics beyond the Standard Model in terms of contact interactions, or from large extra dimensions will modify the observed cross sections for easy to detect final states like lepton or photon pairs, and can be used to probe scales much higher than the center-of-mass energy of the partons initiating the interactions. In this note the sensitivity reach of the Large Hadron Collider to contact interactions in the Drell-Yan channels and of a Future Linear Collider to contact interactions and extra dimensions in , and final states are studied. Experimental aspects of the measurements, systematic error effects and the evolution of the search reach with accumulated luminosity are considered
Search for TeV Strings and New Phenomena in Bhabha Scattering at CERN LEP2
No full textA combined analysis of the data on Bhabha scattering at centre-of-massenergies 183 and 189 GeV from the LEP experiments ALEPH, L3 and OPAL isperformed to search for effects of TeV strings in quantum gravity models withlarge extra dimensions. No statistically significant deviations from theStandard Model expectations are observed and lower limit on the string scaleM_S = 0.631 TeV at 95 onfidence level is derived. The data are used to setlower limits on the scale of contact interactions ranging from 4.2 to 16.2 TeVdepending on the model. In a complementary analysis we derive an upper limit onthe electron size of 2.8 x 10^{-19} m at 95 onfidence level
Study of Parton Density Function Uncertainties with LHAPDF and PYTHIA at LHC
No full textThe experimental errors in current and future hadron colliders are expected to decrease to a level that will challenge the uncertainties in the theoretical calculations. One important component in the prediction uncertainties comes from the Parton Density Functions of the (anti)proton. In this work we develop an interface from the Les Houches Accord Parton Density Functions (LHAPDF) package to the very popular Monte Carlo generator {\tt PYTHIA} version 6.2. Then we proceed to estimate the PDF uncertainties for the production of Drell-Yan pairs from the Z pole to masses above 1 \TeV and for Higgs bosons at LHC. The measurement of the electro-weak mixing angle at LHC as a particularly difficult case is studied
Measurement of the differential and double-differential Drell-Yan cross sections in proton-proton collisions at root s=7 TeV
No full textMeasurements of the differential and double-differential Drell-Yan cross sections are presented using an integrated luminosity of 4.5 (4.8) fb−1 in the dimuon (dielectron) channel of proton-proton collision data recorded with the CMS detector at the LHC at s√ = 7 TeV. The measured inclusive cross section in the Z-peak region (60–120 GeV) is σ(ℓℓ) = 986.4 ± 0.6 (stat.) ± 5.9 (exp. syst.) ± 21.7 (th. syst.) ± 21.7 (lum.) pb for the combination of the dimuon and dielectron channels. Differential cross sections dσ/dm for the dimuon, dielectron, and combined channels are measured in the mass range 15 to 1500 GeV and corrected to the full phase space. Results are also presented for the measurement of the double-differential cross section d2σ/dm d|y| in the dimuon channel over the mass range 20 to 1500 GeV and absolute dimuon rapidity from 0 to 2.4. These measurements are compared to the predictions of perturbative QCD calculations at next-to-leading and next-to-next-to-leading orders using various sets of parton distribution functions
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